1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and an image processing program product which detect a bubble area present in an image, and specifically to an image processing apparatus and an image processing program product which detect a bubble area present in an image captured in a body cavity.
2. Description of the Related Art Japanese Patent Application Laid-Open No. 2004-337596 discloses, as an image processing on an intra-cavity image, a processing of determining an organ based on average color information of an image captured by a capsule endoscope. Specifically, an average value of a red color level and an average value of a blue color level in a pixel of the image are calculated, a discoloration edge position whose amount of change in each color level is not less than a predetermined amount is detected after the calculated values are smoothed in a time-line direction, and a transition of organs is determined in each image among images which are captured by a capsule endoscope and loaded as time-series successive images.
Japanese Patent Application Laid-Open No. 2005-192880 discloses a processing of detecting a diseased site based on color information of each pixel in an image captured by a capsule endoscope. Specifically, each pixel or an averaged pixel value in the image is mapped onto a feature space based on the color information, a cluster for a normal mucous membrane and a cluster for a diseased site are specified after performing clustering in the feature space, and a pixel area classified as the diseased site cluster is detected as a diseased site.
However, since an air bubble (hereinafter simply referred to as “a bubble”) is present in a body cavity captured by a capsule endoscope, it often happens that a bubble as well as a mucous membrane are captured in an intra-cavity image. When a bubble is present in an image, an average value, calculated in Japanese Patent Application Laid-Open No. 2004-337596, of each color level in the image is not a value which adequately reflects an original color level of the mucous membrane due to an influence of the bubble. Thus, an accuracy of an organ determination deteriorates.
Besides, a distribution of a pixel of a bubble area is very wide in the feature space based on the color information and overlaps a distribution of a normal mucous membrane and a diseased site. Therefore, when a detection of a diseased site is performed including pixel information of a bubble area, an accuracy of detection deteriorates in Japanese Patent Application Laid-Open No. 2005-192880, too.
In both of the above cases, as long as a bubble area can be detected in an intra-cavity image, a deterioration in accuracy of an organ determination and a diseased site detection can be suppressed by eliminating a pixel corresponding to the bubble area as an invalid pixel from a subsequent processing. However, the current situation is that no effective solution has been found out to deal with the problem of detecting a bubble area in an intra-cavity image so far.